How to specify "monotonically increasing field"?

On the subject of Dremio reflection incremental refresh, how do you actually specify the “monotonically increasing field”? For example, how do I specify Da_Batt_Mr_Id or Datetime_Utc as the reference field below. Do I mark it as sort or partition?

@RayC

This is only required for non-file system based sources like say Hive/Oracle. Also this has to be set on the REFLECTION REFRESH screen, see attached screenshot below

Many thanks! Much appreciated.